Fig. 2

Preoperative three-dimensional evaluation of tumor components and adjacent structures. a The simulated operative view from the posterior side. The cerebellum is retracted to inspect the floor of the fourth ventricle. A black arrow indicates the obex, and yellow structures indicate the spinothalamic tracts (white double arrows). The asterisk is the cystic component of the tumor bulging into the floor of the fourth ventricle. b The simulated operative view with the translucent brainstem. The pyramidal tract is illustrated by a green line (arrowhead). The asterisk is the same as in (a). The double asterisks indicate the solid component of the tumor. c The actual operative view. The right side in this view is the rostral side of the patient. Before incision of the floor of the fourth ventricle, bilateral facial colliculi were marked by crystal violet after verification with electronic stimulation. The dashed line indicates the patient’s midline. d The orientation of this operative view is the same as in (c). The operator suctioned the solid component of the tumor (double asterisks) using an ultrasonic aspirator